Re: ICC profiles and digi-cam


Andrew Rodney <andrew@...>
 

on 6/18/01 7:50 AM, Lee Varis at varis@... wrote:

White balance for digital camera files is intended to match the color
response of the capture to the color temperature of the light source. It
is relatively easy for manufacturers of digital cameras to build into
their software "developers" a number of different color responses - this
means more choices for the photographer which is mostly a good thing.
White balance is kind of like applying a profile to the "raw" data.
I don¹t agree because I see a huge difference between an input profile and
the role of white balancing. Again, profiles describe color, nothing more.
White balancing affects the response of the color. That¹s a good thing. But
a profile only works when it reflects the capture. That is, if one captures
a file and that method doesn¹t match how a profile was created in the first
place, the profile is invalid. You may end up with perfect ³white balance²
or whatever but when you apply the profile, the results will suffer. So
ideally one gray/white balances and shoots a target like the ColorChecker
DC. Then they build the profile with this gray/white balance in place. It¹s
like ³calibrating² the camera so it¹s capture is consistent and the profile
remains valid. No matter how you gray/white balance (or don¹t), you don¹t
get a description of the RGB data to provide Photoshop 6 without a profile.

The danger is that one can easily overcomplicate the whole thing. You can
create profiles to use with every white balance setting which becomes
sort of like applying profiles on top of profiles.
No, it¹s more like having a slew of profiles to reflect a slew of balances
which is complicated and usually not necessary.

Almost
all digital cameras will perform as well as film does in delivering
neutral color for most scenes even without icc profiles.
Because again, the role of the profile isn¹t to set or alter gray balance.
It¹s only to describe what the camera saw at any given moment. That¹s why
you do want to gray balance and then build a profile. That¹s why after
building the profile, you want to gray balance for each scene. This
accomplishes two things. It insures gray balance (which sometimes you don¹t
want but often do) and it places the capture into a condition that matches
how the original capture was produced to build that profile. So with gray
balance, the profile is valid. The profile will have NO role of the
neutrality of the capture. The profile only records a condition. You have
have a file with a gray and Assign or not assign a profile and the RGB
numbers of the gray will not change a lick.

Once this is done a camera file can be
opened up in Photoshop and assigned any of the standard working spaces
and give you a very reasonable starting place for color.
No! It will only insure you have a neutral gray. If what you say is true,
you could capture the scene as you suggest and Assign sRGB and Wide Gamut
RGB and you¹d get to the same place. Nothing could be further from the
truth. Assigning a profile only describes to Photoshop 6 the MEANING of the
numbers in the file. As you assign different profiles, the numbers NEVER
change. But the preview (and any further conversions FROM the assigned
profile) will change. IF you have a file that is reasonably close to say
ColorMatch RGB, assigning it ColorMatch RGB will work pretty well. Assigning
any space that moves further from ColorMatch RGB will hose the file (Preview
and conversions) farther and farther from the true meaning of the data.
Assuming a digital camera file is in ColorMatch may work or may fail. But if
you actually profile the camera, you know the exact meaning of the numbers.
Realize too that the Working Spaces you can Assign are not based on any real
device. They are synthetic RGB models that work well because they all have
R=G=B as a neutral. You can actually gray balance a digital camera file and
find that this raw capture has data where R, G and B do not equal UNTIL you
convert into the Working Space! Input colorspaces do not insure R=G=B yet
you still have a neutral.

The benefits are not great enough to
warrant the extra trouble either - it is expensive and time consuming to
get a custom profile that would be better than simply assigning a
workspace to a white/gray balanced file for even 50% of the subject
matter you are likely to photograph.
Depends on the camera and what the raw data is. Be my guest and assign any
Working Space to a Nikon D1 image and I assure you they all look like crap.
Assign a custom profile and the color and even tonal range appear much
better because the data was just fine, the preview was hosed in Photoshop 6
because Photoshop 6 didn¹t know what the proper meaning of the raw numbers
were and just assumed whatever RGB Working Space you pick in the color
preferences for untagged data. Raw D1 RGB isn¹t anything like any of the
supplied RGB Working Spaces. You can¹t assume that an input device is
creating RGB that is in any way close to an RGB Working Space you might
have.

For instance, if you manually white balance a sunset scene you will "balance
out" the overall red color and completely destroy the feeling of the
sunset in the image. It is the same thing with profiles.
No, input profiles don¹t change the data, they only describe the data. IF
you built a profile assuming a white balance, you have to white balance.
That act of white balance hoses your sunset, not the profile.

I think the challenge for photographers or anyone dealing with
digital photographic images is to create great images by interpreting
color in the most emotionally satisfying way.
How do you interpret 1¹s and zero¹s? That¹s all a digital file is. That is
why Photoshop 6 needs the proper profile to be assigned. Now you have
properly interpreted the data for Photoshop 6 to provide a correct preview.
You¹ve got the meaning of the numbers necessary to convert to a Working or
Output space. Once you take your ³great² image and Assign the wrong
profile, it¹s not so great anymore, at least visually.

Andrew Rodney


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